The Open Systems Interconnection model (OSI model) for computer networking defines multiple layers on which data can be transferred between networked elements (e.g., systems and devices. The lowest layer of the model, Layer 1 (L1), is defined as the physical layer where bits representing data are transferred over communication links (e.g., as electrical signals over conductive wires). Layer 2 (L2), which is defined as the data link layer, operates on top of L1. L2 provides additional organization for a networked elements. For instance, a L2 network identifies various networked elements based on identifiers, such as Media Access Control (MAC) addresses, for each of those elements. Those identifiers are used as a means for directing data traffic to the proper networked element.
The organizational features of L2 networks also allow distinct L2 networks to operate on a single physical network or across multiple physical networks. The identifiers for networked elements are distinct between the L2 networks and, therefore, allow the L2 networks to remain separate by only being able to exchange network data traffic between certain networked elements. However, there may be situations where an element on one L2 network needs to communicate with an element on another L2 network. In those situations, a network bridge is used to provide a communication bridge between the two L2 networks. Effectively, the network bridge creates a larger aggregate network consisting of the two bridged L2 networks. If for any reason the bridge fails, the aggregate network cannot be maintained and any network traffic that needs to traverse from one L2 network to the other will be undeliverable until a bridge is reestablished.